Risk factors for primary open - angle glaucoma: an epidemiological study

M.Phil.The record cards of all patients (21 554) examined by the eye clinic on the Phelophepa Mobile Health Care train during January and September, 1995 were analysed. The prevalence of. POAG in the sample was 0-.8% (177 of 21 554 persons). Differences in POAG prevalence were observed with respect to sex, age and geographical region. There was a significant difference (p<0.001) in the number of males (1.1%, 92 of 8113), compared to females (0.6%, 85 of 13 441) diagnosed with POAG. In persons over 40 years of age the prevalence rate was 1.2 % (166 of 14 254 persons) and in persons over 60 years the rate was 1.7% (110 of 6375 persons). The highest prevalence rate was found in the Western Cape (1.84%) and the lowest in the Eastern Cape (0.33%). POAG patients were compared to a control group to investigate the role of certain demographic, systemic and ocular factors. Risk factor analysis identified old age(> 60 years) (OR = 7.2, 95% CI = 4.4 - 11.7), geographical area (Western Cape, OR =2.5, 95% CI = 1.7 - 3.9), systolic hypertension (OR = 2.2, 95% CI = 1.3 - 3.7), diastolic perfusion pressure (< 40 mmHg, OR = 12.9, 95% CI = 4.2 - 52.9), myopia (OR = 2.7, 95% CI = 1.7 - 4.4) and elevated IOP (21 - 30 mmHg, OR = 12.6, 95% CI = 6.4 - 25.0) as significant risk factors. The effectiveness of employing certain blood pressure (BP) and intraocular pressure (TOP) variables as screening tools for glaucoma was evaluated. The systolic BP/IOP ratio was the most valid of the four tests evaluated (sensitivity = 66.0%, specificity = 98.2%, phi coefficient = 0.72). The study recommends that glaucoma screening programmes need to be developed which include sphygmomanometry as part of a battery of tests, and these programmes be targeted specifically at high risk populations (elderly, hypertensives). Further epidemiological studies are required which investigate reasons for the geographical differences found with respect to glaucoma prevalence